no really, use mapConcurrently

src/Tahoe/Download.hs

@@ -123,7 +123,7 @@ executeDownloadTasks ::
     -- | The results of all successful downloads.
     m [DownloadedShare]
 executeDownloadTasks storageIndex tasks = do
-    downloadResults <- mapM (downloadShare storageIndex) tasks
+    downloadResults <- liftIO $ mapConcurrently (downloadShare storageIndex) tasks
     pure . rights $ inject <$> downloadResults
   where
     inject (a, b) = (a,) <$> b